Overload friction coupling

ABSTRACT

The overload friction coupling employs a tubular sleeve having an axial abutment and clamping nut securing therebetween two opposed Bellville springs, a spring carrier, two pairs of expanding and contracting wedge rings, and a spacer washer between the rings. With the axial clamping pressure of the Bellville springs, the rings will contract into engagement with the sleeve and simultaneously expand into engagement with the inner cylindrical surface of a spur gear. With the sleeve keyed to a motor shaft, the spur gear is securely supported at its opposite axial ends, due to the spacer ring, along cylindrical bearing and torque transmitting surfaces. The torque at which the coupling will slip, that is provide relative rotational movement between the gear and shaft, is predetermined by the axial pretensioning of the Bellville springs, which in turn is determined by the degree to which the adjusting nut is threaded on to the sleeve.

United States Patent Garcia, ,lr.

[54] OVERLOAD FRICTION COUPLING [72] Inventor: Roger Garcia, Jr.,Pittsfield, Mass.

[73] Assignee: General Electric Company [22] Filed: June 1, 1970 [21]Appl. No.: 42,285

[52] US. Cl ..64/30 [51] ...F16d 7/02 58] Field of Search ..64/ 30 [56]References Cited UNlTED STATES PATENTS 2,763,141 9/1956 Dodge ..64/702,901,912 9/1959 Digby ...64/30 X 2,127,768 8/1938 Debrie ..64/30 RAPrimary Examiner-Edward G. Favors [57] ABSTRACT The overload frictioncoupling employs a tubular sleeve having an axial abutment and clampingnut securing therebetween two opposed Bellville springs, a springcarrier, two pairs of expanding and contracting wedge rings, and aspacer washer between the rings. With the axial clamping pressure of theBellville springs, the rings will contract into engagement with thesleeve and simultaneously expand into engagement with the innercylindrical surface of a spur gear. With the sleeve keyed to a motorshaft, the spur gear is securely supported at its opposite axial ends,due to the spacer ring, along cylindrical bearing and torquetransmitting surfaces. The torque at which the coupling will slip, thatis provide relative rotational movement between the gear and shaft, ispredetermined by the axial pretensioning of the Bellville springs, whichin turn is determined by the degree to which the adjusting nut isthreaded on to the sleeve.

11 Claims, 1 Drawing Figure Patented March 14,. 1972 3,648,483

I l3 l4 As% 2 W l8 INVENTOR ROGER GARCIA JR.

HIS ATTORNEY OVERLOAD FRICTION COUPLWG BACKGROUND OF THE INVENTIONOverload friction couplings are well known, but usually components sothat their addition to a standard torque transmitting element in a powertrain would considerably increase the dimensional requirements of theelement and result in excessively high increase in the cost of theelement. Such overload friction slip couplings are highly desirable oreven necessary in power trains employed for many different purposes, forexample in the power train for rotating a tank turret to preventbreakage in the event that the turret or a projection therefrom strikesan immovable object during rotation.

One known example of a prior art friction coupling having considerablespace requirements and complexity employs a roller bearing forsupporting a power train member, a sprocket, on a shaft with radiallyextending opposed plates frictionally clamping the sprocket with apredetermined overload torque value as determined by a pair of opposedBellville springs pretensioned by a threaded nut. Considering therelatively narrow width of the sprocket, the side friction plates takeup a considerable amount of room and the necessity of requiring separatebearings considerably increases the cost and complexity of the device.

Wedging rings have been used in the past in overload couplings, forexample the Debn'e US. Pat. No. 2,127,768, issued Aug. 23, 1938, but fora controlled spring clamping pressure, the spring loading mechanismshave required a considerable amount of space, for example as seen in theHansen U.S. Pat. No. 1,373,810, issued Apr. 5, 1921.

Many power trains employ gears mounted on a shaft, which gears must havea predetermined tooth width to transmit the desired torque and a gearmounting that will provide secure support for the gear without unduecanting or vibrations with respect to the shaft. Usually, power trainsor transmissions are compactly constructed due to a space premium sothat the splitting of the shaft to provide an overload couplingconsiderably increases the complexity and space requirements of thetransmission.

SUMMARY It is an object of the present invention to overcome thedisadvantages in the prior art with respect to overload frictioncouplings, particularly, by providing a friction coupling that may bemounted in a minimum of space without unduly increasing the complexityof the device with which it is associated. Particularly, the coupling iswell suited to be mounted between a transmission drive member,preferably a gear, and its supporting shaft. Besides providing torquetransmittal between the shaft and the gear, the coupling of the presentinvention supports the gear about its inner periphery at axially spacedareas, particularly its axially opposite ends to concentrate the radialforce at the axial ends of the gear to minimize canting and vibrationwith respect to the mounting shaft. Further, the coupling provides themounting for the gear and the bearing for relative movement between thegear and its associated shaft, which bearing automatically compensatesfor any wear by being self-adjusting both inwardly and outwardly in theradial direction.

The coupling of the present invention employs two pairs of wedging ringsthat are axially spaced by a noncontracting and non-expanding washer.For each pair, an outer wedge ring is provided for expansion against aninner cylindrical surface of the gear to provide for radial torquetransmittal and to provide a radial bearing, and an inner wedge ringthat will contract into engagement with the cylindrical surface of asleeve carried by a shaft to provide radial torque transmittal and toprovide a radial hearing. The wedge rings of each pair are provided withcooperating frustoconical wedge surfaces that will produce the expansionand contraction upon being axially clamped by a pair of opposedBellville springs pretensioned by a nut threaded on the sleeve.

Conventional, releasable mountings between a gear and a shaft will havea predetermined axial space requirement; the coupling of the presentinvention will have the same axial space requirements, or will be onlyslightly greater. The coupling of the present invention will not produceany additional radial space requirements. Bellville springs arepreferred for their ability to provide a constant preloading over a widetemperature range, their minimum axial space requirements, and theirwide range of axial force production over a relatively short axialdeflection range. Because of the cooperation between the Bellvillesprings and wedge rings with cylindrical bearing surfaces, the torqueresponse for the coupling of the present invention is substantiallylinear over a wide range of nut adjustment, and substantially constantfor any particular adjustment over a wide range of environmenttemperatures. The main space requirement of the Bellville springs is inthe radial direction, where space is normally available due to theradial extent of one of the coupled members, particularly a spur gear.

While the overload coupling of the present invention may be used betweenany torque transmitting members, it is particularly advantageous withrespect to a spur gear due to its minimum increased space requirementsas compared to the usual coupling for a spur gear on a shaft, its widelyaxially spaced circumferential pressure areas that will provide a rigidsupport for the gear with respect to rocking or canting of the gearabout an axis transverse to the shaft, and the dual function in thecylindrical coupling surfaces of the rings with respect to providingradial plain bearings.

BRIEF DESCRIPTION OF THE DRAWING Further objects, features andadvantages in the present invention will become more clear with respectto the following detailed description of a preferred embodiment shown inthe attached drawing.

The single FIGURE of the drawing is a cross-sectional view taken in aplane passing through the axis of rotation of the power transmissionshaft.

DETAILED DESCRIPTION OF THE DRAWING While specific structural details ofa preferred embodiment will be described, which are of considerableimportance in their own right, it is contemplated that the broaderaspects of the present invention may take different forms, particularlywith respect to further embodiments, variations and modifications. Asshown in the drawing, the overload friction coupling is employed betweena power transmission motor shaft 1 and a spur gear 2 having a pluralityof peripherally arranged gear teeth 3.

For mounting purposes, the shaft 1 is provided with a reduced diameterportion 4 forming an axially facing shoulder 5 in axial abuttingengagement with the right hand axial end of a generally tubular sleeve 6telescopically received on the reduced diameter portion 4. The sleeve 6and shaft 1 are rotational coupled together by conventional key 7 andwithdrawal of the sleeve 6 in the left hand direction, as viewed in thedrawing, is prevented by conventional] snap ring 8. It is contemplatedthat the sleeve 6 may be secured to a shaft 1 by other means, forexample, a shrink fit or welding.

At one axial end, sleeve 6 is provided with an external thread 9 and atits other axial end, it is provided with an outwardly extending annularabutment flange or collar 10 which has an axially facing radial abutmentface 11. Between the thread 9 and the flange 10, the outer surface ofthe sleeve 6 is cylindrical, which surface cooperates with an innercylindrical surface 12 of the gear 2 to form an annular couplingchamber. The shaft 1, sleeve 6, key 7 and snap ring 8 together form onerotatable member for cooperation with the other rotatable memberconstituted by the gear 2. Either rotatable member may be the drivemember with the other being the driven member.

For torque transmittal and joumaling between the gear 2 and sleeve 6,there are provided two axially spaced pairs of wedge rings. One pair ofwedge rings includes an inner wedge ring 13 having an inner cylindricalsurface in engagement with the outer cylindrical surface of the sleeve6, a radially extending abutment surface in engagement with a plaincircumferentially integral spacer washer 14, and a frustoconical orwedge surface in engagement with a correspondingly spaced frustoconicalwedge surface on the outer ring 15 of the same pair, which outer ring 15has a radially extending abutment surface in engagement with a face 11on abutment of the sleeve 6 and a cylindrical outer surface inengagement with the cylindrical inner surface 12 of the gear 2. Theother wedge ring pair includes an inner wedge ring 16 that is identicalto the inner wedge ring 13 to reduce its manufacturing cost and has itsradially extending surface in engagement with a radially extending face17 of an annular spring carrier 18. The outer wedge ring 19 of thissecond pair is preferably identical to the outer wedge ring 11 to reducemanufacturing cost and has its radially extending surface in engagementwith the other side of the spacer washer 14. While each wedge ring 13,15, 16, 19 in this particular embodiment is of a circumferentiallycontinuous construction, each of said wedge rings could also becircumferentially discontinuous only at a single narrow gap, which mayextend axially or at an angle thereto.

For applying and adjusting the torque transmitting pressures, a lock oradjusting nut 20 is screwed onto the threaded portion 9 of sleeve 6 toaxially pretension an opposed or backto-back pair of Bellville springs21, which springs are in turn concentrically mounted on the springcarrier 18. The axial force produced by the pretensioning of the springs21 is transmitted by the carrier 18 to axially clamp the wedge rings 13,15, 16, 19 and spacer washer 14 against the face 11 of the flange 10.This axial clamping force is radially directed by the wedging orfrustoconical surfaces of the wedge rings to expand the outer rings and19 against the cylindrical inner surface 12 of the gear 2, and tocontact the inner wedge rings 13, 16 against the adjacent cylindricalouter surface of the sleeve 6. The force of this radial expansion andcontraction is correlated to and adjusted by the degree to which the nut20 is screwed onto the sleeve 6, that is the degree to which theBellville springs 21 are pretensioned.

From the above, it is seen that the gear 2 is mounted on the sleeve 6 bycylindrical bearing surfaces that are axially spaced with respect toeach other as determined by the spacer washer 14, which will preventcanting or rocking of the gear 2 about an axis transverse to theshaft 1. Even after repeated slippage or other wear, this bearing willstill be tight due to the self-adjusting nature of the pretensionedsprings 21 and wedge rings. Thus, this bearing will be even tighter thana normal plain radial bearing in that it is radially pretensioned.Further, the torque transmittal is radially accomplished by means of thepretensioned wedge rings and equally divided along the two axiallyspaced positions to evenly distribute the torque to the gear to furtherassure vibration free mounting of the gear with the advantages of arigid coupling and a resilient coupling.

Due to the circumferentially integral nature of the ring 14 and a slightradial spacing between the ring 14 and both the cylindrical surface 12of the gear 2 and the outer cylindrical surface of the sleeve 6, thespacer washer 14 will not transmit any radial torque, although it isfree to rotate on the sleeve 6 for providing a balancing of the torquetransmitted between the ring pairs. In this manner, the net radialforces on the spacer washer 14 will be substantially balanced due to thefact that one adjacent ring is contracting while the other adjacent ringis expanding and the engaging surfaces therebetween are radiallyextending.

Actual test results have shown that the slip torque level for a givenaxial load is consistent from one test to another, even under extremetemperature fluctuations. These consistent results are particularly dueto the nature of the constant axial load produced for one adjustingposition of the Bellville springs. For example, at 70 F. a test couplingslipped at a torque of 400 inch-pounds; at F the test coupling slippedat a torque of 410 inch-pounds; and at 200 F. the test coupling slippedat a torque of 380 inch-pounds. Over this relatively wide range oftemperature fluctuations, the torque transmittal limit remainedsubstantially constant. Even at the extreme temperature of 35 F., themaximum torque transmitted, or point of slippage occurred at 290inch-pounds. It is contemplated that even better results can be obtainedwith special purpose lubricants between the rings and their associatedelements. Further tests showed that the slip torque level is linear withaxial load. Specific results were obtained with an axial load varyingbetween 200 and l,600 pounds for a single coupling, which produced acorresponding variation in slip torque between 50 inch-pounds and 400inch-pounds, for eight successive substantially equal increment loadvariations.

Thus, it is seen that the overload friction coupling of the presentinvention derives space requirement advantages, substantially constantslip torque values over a wide temperature range, and a slip torque thatvaries linearly with adjusted axial load by the use of Bellville springsin cooperation with wedge rings. The wedge rings do not have anyincreased space requirements over those of a conventional gear mounting,and provide for an advantageous axially spaced distribution of theradial torque transmittal, a self-adjusting bearing, a vibrationdampening bearing having axially spaced pressure points and a minimumnumber of parts for producing torque overload.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. An overload friction coupling having an axis of rotation, comprising:a first rotatable member having an outer friction coupling surface; asecond rotatable member having an inner friction coupling surfaceopposite said outer surface; at least one pair of inner and outer,contracting and expanding respectively, wedge ring constituting meansfor frictionally engaging between said outer and inner surfaces totransmit torque between said members when subjected to an axial clampingpressure; and Bellville spring means for exerting an axial clampingpressure on said rings, said Bellville spring means including a springcarrier ring having a tubular portion telescopically received on saidfirst rotatable member and a Bellville spring mounted on said tubularportion, said carrier ring having an outer annular flange radiallyoverlapping said Bellville spring between said spring and said wedgerings.

2. An overload friction coupling having an axis of rotation, comprising:a first rotatable member having an outer friction coupling surface; asecond rotatable member having an inner friction coupling surfaceopposite said outer surface; at least one pair of inner and outer,contracting and expanding respectively, wedge rings constituting meansfor frictionally engaging between said outer and inner surfaces totransmit torque between said members when subjected to an axial clampingpressure; and Bellville spring means for exerting an axial clampingpressure on said rings; said surfaces being cylindrical; said ringsincluding two pairs of rings; said first rotatable member including ashaft, a sleeve having said outer cylindrical surface, a threadedportion on said sleeve and an axial abutment on said sleeve, key meansdrivingly securing said sleeve on said shaft, axial abutment meanspreventing relative movement between said shaft and sleeve; saidBellville spring means including a spring carrier ring having a tubularportion telescopically received on said tubular portion, said carrierring having an outer annular flange radially overlapping said Bellvillespring between said spring and said wedge rings.

3. An overload friction coupling, comprising: a gear member having aplurality of external teeth and an inner surface; a rotatable memberconcentrically received within said gear member and having an outersurface substantially coextensive with and opposite from said gearmember surface; said outer and inner surfaces being spaced from eachother in the radial direction to form therebetween an annular chamberhaving opposed axial ends; an axial abutment at one axial end of saidchamber and being drivingly connected to one of said members; a firstpair of bearing and wedge rings at one axial end of said chamberdirectly engaging between said gear member inner surface and saidrotatable member outer surface for respective expansion and contractionwhen subjected to an axial clamping pressure; a second pair of bearingand wedge rings at the other axial end of said chamber directly engagingbetween said gear member inner surface and said rotatable member outersurface for respective expansion and contraction when subjected to anaxial clamping pressure; non-expanding and non-contracting spacing meansbetween said first and second pairs, and being mounted for free axialmovement without radial torque transmittal for spacing the radialpressure of said pairs at opposite ends of said gear member; and commonmeans for providing an axial force for clamping said first and secondring pairs and spacing means against said axial abutment.

4. The coupling of claim 3, wherein said common means includes athreaded clamping nut, and two mirror image Bellville springs axiallybetween said nut and said ring pairs.

5. The coupling of claim 4, including an annular spring carrier having atubular portion mounting thereon said Bellville springs and an outerflange axially between said Bellville springs and said ring pairs.

6. The coupling of claim 3, wherein the opposite axial ends of saidteeth are substantially radially aligned with the 0pposite axial ends ofsaid ring pairs and chamber.

7. The coupling of claim 3, wherein said inner and outer surfaces arecylindrical.

8. The coupling of claim 7, wherein each pair of rings includes a firstwedge ring having an outer cylindrical surface in direct engagement withsaid gear member inner cylindrical surface, a radially extending sidesurface and a frustoconical wedge surface, and a second wedge ringhaving an inner cylindrical surface in engagement with said outercylindrical surface of said rotatable member, a radially extending sidesurface and a frustoconical wedge surface in engagement with saidfirst-mentioned frustoconical wedge surface; and said spacer ring havingopposed radially extending faces in engagement with the radiallyextending side surface of the adjacent ring of each pair of rings.

9. The coupling of claim 8, Wherein said axial abutment has a radiallyextending side face in engagement with the radially extending sidesurface of the adjacent ring of one pair; and said common meansincluding a portion having a radially extending face in engagement withthe radially extending surface of the adjacent ring.

10. The coupling of claim 9, wherein the radially extending faces ofsaid axial abutment and common means are in substantially radialalignment with the respective opposite axial ends of said gear member.

l L An overload friction coupling comprising a first member rotatableabout an axis and having an outer friction coupling surface which is asurface of revolution about said axis; a second member rotatable aboutthe same axis and said first member and having an inner frictioncoupling surface uniformly spaced from said outer surface to form achamber; two pair of contracting and expanding wedge rings centered onsaid axis and lying within said chamber for permitting frictional drivebetween said rings and members, each said pair of rings having an innerand outer annular ring, said inner ring being in contact with said outersurface and said outer ring being in contact with said inner surface,said rings of each pair being in contact with each other through matingfrustoconical surfaces; an annular free-floating spacer washer alsolocated in said chamber centered on said axis between said pairs wherebyeach pair of rings is maintained proximate to a different remote axialend of said members; and spring means exerting clamping pressure axiallyof said device to force said rings into a predetermined frictionalcontact with each other and with said inner and outer surfaces; saidspring means ineluding shoulder means on one said member at one axialend of said chamber to provide abutment means for said ring closest thatend, spring carrier means at the other axial end of said chamber havinshoulder means roviding abutment means for said ring c osest that endand a utrnent means for a Bellville spring, adjustable stop means alsoattached to said one member and at least one Bellville spring betweensaid stop means and said abutment means for said spring whereby saidspring may be made to exert pressure on said rings axially of saiddevice wedging said rings and said surfaces into frictional contact witheach other.

i i 4k

1. An overload friction coupling having an axis of rotation, comprising:a first rotatable member having an outer friction coupling surface; asecond rotatable member having an inner friction coupling surfaceopposite said outer surface; at least one pair of inner and outer,contracting and expanding respectively, wedge rings constituting meansfor frictionally engaging between said outer and inner surfaces totransmit torque between said members when subjected to an axial clampingpressure; and Bellville spring means for exerting an axial clampingpressure on said rings, said Bellville spring means including a springcarrier ring having a tubular portion telescopically received on saidfirst rotatable member and a Bellville spring mounted on said tubularportion, said carrier ring having an outer annular flange radiallyoverlapping said Bellville spring between said spring and said wedgerings.
 2. An overload friction coupling having an axis of rotation,comprising: a first rotatable member having an outer friction couplingsurface; a second rotatable member having an inner friction couplingsurface opposite said outer surface; at least one pair of inner andouter, contracting and expanding respectively, wedge rings constitutingmeans for frictionally engaging between said outer and inner surfaces totransmit torque between said members when subjected to an axial clampingpressure; and Bellville spring means for exerting an axial clampingpressure on said rings; said surfaces being cylindrical; said ringsincluding two pairs of rings; said first rotatable member including ashaft, a sleeve having said outer cylindrical surface, a threadedportion on said sleeve and an axial abutment on said sleeve, key meansdrivingly securing said sleeve on said shaft, axial abutment meanspreventing relative movement between said shaft and sleeve; saidBellville spring means including a spring carrier ring having a tubularportion telescopically received on said tubular portion, said carrierring having an outer annular flange radially overlapping said Bellvillespring between said spring and said wedge rings.
 3. An overload frictioncoupling, comprising: a gear member having a plurality of external teethand an inner surface; a rotatable member concentrically received withinsaid gear member and having an outer surface substantially co-extensivewith and opposite from said gear member surface; said outer and innersurfaces being spaced from each other in the radial direction to formtherebetween an annular chamber having opposed axial ends; an axialabutment at one axial end of said chamber and being drivingly connectedto one of said members; a first pair of bearing and wedge rings at oneaxial end of said chamber directly engaging between said gear memberinner surface and said rotatable member outer surface for respectiveexpansion and contraction when subjected to an axial clamping pressure;a second pair of bearing and wedge rings at the other axial end of saidchamber directly engaging between said gear member inner surface andsaid rotatable member outer surface for respective expansion andcontraction when subjected to an axial clamping pressure; non-expandingand non-contracting spacing means between said first and second pairs,and being mounted for free axial movement without radial torquetransmittal for spacing the radial pressure of said pairs at oppositeends of said gear member; and common means for providing an axial forcefor clamping said first and second ring pairs and spacing means againstsaid axial abutment.
 4. The coupling of claim 3, wherein said commonmeans includes a threaded clamping nut, and two mirror image Bellvillesprings axially between said nut and said ring pairs.
 5. The coupling ofclaim 4, including an annular spring carrier having a tubular portionmounting thereon said Bellville springs and an outer flange axiallybetween said Bellville springs and said ring pairs.
 6. The coupling ofclaim 3, wherein the opposite axial ends of said teeth are substantiallyradially aligned with the opposite axial ends of said ring pairs andchamber.
 7. The coupling of claim 3, wherein said inner and outersurfaces are cylindrical.
 8. The coupling of claim 7, wherein each pairof rings includes a first wedge ring having an outer cylindrical surfacein direct engagement with said gear member inner cylindrical surface, aradially extending side surface and a frusto-conical wedge surface, anda sEcond wedge ring having an inner cylindrical surface in engagementwith said outer cylindrical surface of said rotatable member, a radiallyextending side surface and a frusto-conical wedge surface in engagementwith said first-mentioned frusto-conical wedge surface; and said spacerring having opposed radially extending faces in engagement with theradially extending side surface of the adjacent ring of each pair ofrings.
 9. The coupling of claim 8, wherein said axial abutment has aradially extending side face in engagement with the radially extendingside surface of the adjacent ring of one pair; and said common meansincluding a portion having a radially extending face in engagement withthe radially extending surface of the adjacent ring.
 10. The coupling ofclaim 9, wherein the radially extending faces of said axial abutment andcommon means are in substantially radial alignment with the respectiveopposite axial ends of said gear member.
 11. An overload frictioncoupling comprising a first member rotatable about an axis and having anouter friction coupling surface which is a surface of revolution aboutsaid axis; a second member rotatable about the same axis and said firstmember and having an inner friction coupling surface uniformly spacedfrom said outer surface to form a chamber; two pair of contracting andexpanding wedge rings centered on said axis and lying within saidchamber for permitting frictional drive between said rings and members,each said pair of rings having an inner and outer annular ring, saidinner ring being in contact with said outer surface and said outer ringbeing in contact with said inner surface, said rings of each pair beingin contact with each other through mating frusto-conical surfaces; anannular free-floating spacer washer also located in said chambercentered on said axis between said pairs whereby each pair of rings ismaintained proximate to a different remote axial end of said members;and spring means exerting clamping pressure axially of said device toforce said rings into a predetermined frictional contact with each otherand with said inner and outer surfaces; said spring means includingshoulder means on one said member at one axial end of said chamber toprovide abutment means for said ring closest that end, spring carriermeans at the other axial end of said chamber having shoulder meansproviding abutment means for said ring closest that end and abutmentmeans for a Bellville spring, adjustable stop means also attached tosaid one member and at least one Bellville spring between said stopmeans and said abutment means for said spring whereby said spring may bemade to exert pressure on said rings axially of said device wedging saidrings and said surfaces into frictional contact with each other.